1. Field of the Invention
The present invention relates to waste processing systems and more particularly to waste processing systems for processing consumer waste (see DEFINITIONS section).
2. Description of the Related Art
Conventionally, one of the most common methods of disposing of consumer wastes is the deposition of such wastes on land or in landfills. In the United States, such landfills generally are the repositories of more than ninety percent of consumer waste. In the United States, incineration is another conventional waste processing method. Incineration is used to dispose of most of the remaining ten percent of consumer waste. Another conventional waste processing method is composting. Composting of solid wastes is currently utilized in only insignificant amounts in the United States.
Given the above, the general viewpoint is that a properly designed landfill is the cheapest satisfactory means of disposal for consumer waste. However, this is only the case if suitable land is located within a convenient range of the source of the consumer waste. Typically, collection and transportation costs account for approximately seventy-five percent of the total cost of consumer waste management. The transportation cost is likely to rise in the future, with rising energy costs, and thereby make landfill disposal relatively more expensive.
In modern landfills, consumer waste is usually spread in thin layers, each of which is compacted by heavy industrial equipment, such as bulldozers, before the next layer is spread on top. When about 3 meters of consumer waste has been laid down, it is covered by a thin layer of clean earth, which is then also compacted. Pollution of surface and groundwater is generally managed by lining and contouring the fill, compacting and planting suitable cover, selecting proper soil, diverting upland drainage, and placing wastes in sites not subject to flooding or high groundwater levels. As is known, certain gases are generated in landfills due to the anaerobic decomposition of organic consumer waste. Since some of these gases are explosive in nature (for example, methane), it is important that such landfills have proper ventilation and/or methane disposal or capture systems.
Moving from landfill disposal to incineration disposal, incinerators of conventional design burn consumer waste on moving grates in refractory-lined chambers. The combustible gases and the solids they carry are burned in secondary chambers. Combustion is eighty-five to ninety percent complete for any combustible materials present in the waste stream. In addition to heat, the products of incineration include the normal primary products of combustion including carbon dioxide and water, as well as oxides of sulfur and nitrogen and other gaseous pollutants. The non-gaseous products produced by incineration are fly ash and unburned solid residue. Emissions of fly ash and other particles are often controlled by wet scrubbers, electrostatic precipitators, and bag filters.
Therefore, landfill-based and incineration-based waste processing processes create significant environmental problems and concerns for any municipality, government, private industry, and/or individual involved in waste management activities. In light of the problems associated with the use of landfills and incineration methods, a trend has developed whereby the treatment and handling of consumer waste involves “resource recovery” type waste processing processes. Resource recovery waste processing systems attempt to recover useful materials from consumer waste and may include grinding or shredding machines, magnetic separators, air classification that separates the light and heavy fractions, screening, and/or washing. In other words, resource recovery type waste processing attempt to reduce (that is, recycle) the solid waste into a more manageable form, although this reduced form often has little to no practical utility.
Resource recovery waste processing can be generally considered as a thermal process. More specifically, it is a combustion process and/or a pyrolysis process. Pyrolysis, also called destructive distillation, is the process of chemically decomposing consumer wastes by the introduction of heat in an oxygen-reduced atmosphere. This process yields a gas stream containing primarily hydrogen, methane, carbon monoxide, carbon dioxide, and various other gases and inert ash, depending on the organic characteristics of the material being pyrolyzed.
One conventional resource recovery type of waste processing process for consumer waste is wet pulping process. In wet pulping process the incoming refuse is mixed with water and ground into a slurry in an apparatus referred to as a wet pulper, which is a machine similar to a large kitchen disposal unit. Large pieces of metal and other non-pulpable materials are separated by a magnetic separator, and the residue is used as fill. The slurry from the pulper goes into a centrifugal device called a liquid cyclone, which separates heavier non-combustibles such as glass, metals, and ceramics. The heavy portion of the slurry goes to a glass and metal recovery system. The lighter portion goes to a paper and fiber recovery system. Combustible residues are mixed with sewage sludge, mechanically dewatered, and incinerated. Noncombustible residues are used as fill.
U.S. Pat. No. 5,340,036 (“Riley”) discloses a grinder for a sink opening that includes an upper grinding section and a rotatable shredder component.
According to U.S. Pat. No. 5,705,216 (“Tyson”), a Canadian company, Stake Technology, has used a modified version of steam explosion to delignify lignocellulosic material.
U.S. Pat. No. 5,772,134 (“Bouldin 1”) discloses a grinding apparatus including a grinder for reducing the size of waste material, a series of conveyors, a shredder and at least one magnetic device.
U.S. Pat. No. 6,290,885 (“Roetheli”) is directed to a waste processing system including steam explosion processing and the addition of plastic to the processing waste (see DEFINITIONS section). However, as Roetheli is understood, the plastic is added to the processing waste subsequent to the steam explosion process step.
U.S. Pat. No. 6,627,676 (“George”) is directed to a waste processing system including plastic and a steam explosion process step. However, the plastic is added to the processing waste subsequent to the steam explosion process step.
U.S. Pat. No. 7,101,164 (“Bouldin 2”)  discloses a pressure vessel apparatus in the general nature of a hydrolyzer used for the reduction, decomposition, destruction and/or conversion (hereinafter “rendering”) of organic wastes generated during meat and poultry production for human consumption.
An article entitled “Extrusion of Alternative Ingredients: An Environmental and a Nutritional Solution,” by Nabil W. Said (the “Extrusion Article”), discloses that material has been processed in a dry extruder at elevated temperature and pressure so that cells are ruptured when the material leaves the extruder. According to the Extrusion Article, materials that have been processed in this manner include feathers, offal, turkey litter, broiler litter, partially dehydrated layer manure, farm mortalities, dissolved air flotation, restaurant grease, fish waste, eggshells, unsalable eggs, cheese trimmings, tallow and other food industry by-products.
Description Of the Related Art Section Disclaimer: To the extent that specific publications are discussed above in this Description of the Related Art Section, these discussions should not be taken as an admission that the discussed publications (for example, published patents) are prior art for patent law purposes. For example, some or all of the discussed publications may not be sufficiently early in time, may not reflect subject matter developed early enough in time and/or may not be sufficiently enabling so as to amount to prior art for patent law purposes. To the extent that specific publications are discussed above in this Description of the Related Art Section, they are all hereby incorporated by reference into this document in their respective entirety(ies).